Osteoporosis has continued to be a ubiquitous problem, especially in our elderly population. It is said that osteoporosis sufferers outnumber patients in the United States who have had MI's, stroke, and breast cancer combined. Osteoporosis can result in compression fractures of the vertebral bodies of the spinal column. As shown in FIG. 1, these fractures 10 generally occur in the anterior portion of the vertebra, with this portion compressing to a smaller height than a normal vertebral body. With increasing numbers of osteoporotic compression fractures of the thoracic and lumbar spine, it is felt that 1 in 3 women and 1 in 5 men will have an osteoporotic fracture in their lifetime. By the date 2020, osteoporosis is expected to affect approximately 14 million people in the United States. These fractures become more common obviously in older population and current treatment recommendations include vertebroplasty which can be done as an outpatient and kyphoplasty, which requires an in hospital stay of approximately one day.
PMMA, poly methacrylate, is the substance used in both vertebroplasty and kyphoplasty. This material has been used throughout orthopedics for over 35 years. The first total hip replacements done by Dr. Charnley in Boston and utilized a methacrylate. This material is also known as bone cement and its modulus of elasticity is much higher than that of cancellous or cortical bone. When this material is placed into a vertebral body and is allowed to cure, it creates an exothermic reaction, which can sometimes deaden or destroy nociceptin fibers and once it is hardened, it provides rigid support of the vertebra. Unfortunately, the remaining part of the vertebra and the part in which the cement has been placed cannot grow new bone. The exothermic reaction, if it is close to the endplate, can cause avascular necrosis and result in endplate fracture and adjacent segment collapse. Some of the issues that are associated with the use of PMMA include, but are not limited to, cord compression from ectopic cement extending from the vertebral body into the spinal canal, extrusion of cement through the cartilaginous endplate into the disc, allergic reaction to PMMA, coagulopathy, PMMA getting into the basivertebral sinus resulting in pulmonary emboli and infection because of the foreign body. These are some of the related complications that can occur with vertebroplasty or kyphoplasty. Furthermore, what we have seen over the years is that the cement, which does decrease pain, also appears to cause adjacent segment fractures at a later date. Some as early as a few months and others within a few years. The reason for these compression fractures is: 1) Underlying osteoporosis throughout the vertebral bodies. 2) Cement having a higher density than the cortical or cancellous bone and adjacent microfracturing, which may not have been detected at the time of the initial procedure involving the adjacent vertebra. In addition, compression fractures at TS or above are technically difficult due to the small pedicle and the parallel orientation of these pedicles. The thoracic spine is also very vulnerable in the event the cement is extruded, which could result in myelopathy or paresis or plegia.